Transfer Functions of Wireless Power Transfer Systems with Series and Series-Parallel Compensation Schemes

This paper presents the transfer functions of the ac circuit in wireless power transfer (WPT) systems. The series-primary and series-parallel-secondary type of compensation schemes are considered. The equivalent cantilever model of the transformer in terms magnetizing and leakage inductances is developed. The following transfer functions are derived: (a) voltage gain, (b) current gain, (c) input impedance, and (d) power transfer efficiency. Design example for both types of compensated WPT system is given. The impact of pole-splitting phenomena on power transfer efficiency at different coupling coefficients is addressed. The frequency-domain analysis of the WPT systems is performed. Characteristic differences of the WPT system using the two compensation schemes are reported and benefits of each scheme are identified.